The present invention relates to methods and systems for enabling data packets to be routed through a wireless network, where the network comprises a number of individual wireless transceivers configured to enable data packets to move or hop from one wireless transceiver or node to another until they reach a given destination. More particularly, the present invention includes a routing protocol that uses a modified link-state routing algorithm to make fast routing computations and reverse-path-lookup rules to prevent broadcast loops.
A trend in distributed networks is the proliferation of wireless applications for voice, fax, paging, data, images, and video. The use of these wireless applications is expanding to true global coverage through the use of satellite networks and in-flight data communications services on commercial airlines. These wireless networks generally have lower bandwidths and higher error rates than traditional wired networks. One type of wireless network in particular, the “ad-hoc,” or Mobile Ad-Hoc Network (MANET) is particularly sensitive to these issues. MANETs are networks that may be deployed rapidly with little or no assistance and that do not have a central network structure, such as cellular-base stations or overhead satellite assets. The nodes within the MANETs are typically highly mobile and use a variety of wireless network platforms. Furthermore, nodes within the MANET may dynamically enter or leave the network. Therefore, the number of nodes and the disposition of nodes within the MANET are highly fluid and are often continually changing. By their nature, MANETs complicate the design and implementation of acceptable protocols to support communications between nodes within the network.
The configuration of an ad-hoc network typically is either hierarchical or flat. In a hierarchical ad-hoc network, the network nodes are partitioned into groups called clusters. Within each cluster, one node is chosen to be a “cluster head.” In contrast, the nodes in a flat ad-hoc network are all equal. Connections are established between nodes that are in close enough proximity to one another to allow sufficient radio propagation conditions to establish connectivity. Routing between nodes is constrained by the connectivity conditions, and possibly by security limitations. In the general case, a network may use a hybrid approach wherein a cluster-based topology is used for routing-control traffic but a flat network topology is used for the actual user-data traffic.
Ad hoc networking introduces several important difficulties for traditional routing protocols. First, determining a packet route requires that the source node know the reachability information of its neighbors. Second, the network topology may change quite often in an ad-hoc network. As the number of network nodes increases, the potential number of destinations becomes large, requiring large and frequent exchanges of data (e.g., routes, route updates, or routing tables) among the network nodes. Updates in the wireless communication environment travel over the air, and therefore consume a great deal of network resources. As the network size increases and as the nodal mobility increases, smaller and smaller fractions of this total amount of control traffic are of practical usefulness. This is due to the fact that, as the nodes become more mobile, the lifetime of a link decreases, and the period in which the routing information remains valid decreases as well. It is easy to see that, for any given network capacity, there exists a network size and nodal mobility which would result in having all the network capacity wasted on control traffic.
Existing IP routing protocols that manage wireless networks can be classified either as proactive or as reactive. Proactive protocols attempt to continuously evaluate the routes within the network, so that when a packet needs to be forwarded, the route is already known and can be used immediately. The Optimized Link State Routing Protocol (OLSR) is one example of such a proactive scheme known to persons of ordinary skill in the art. Reactive protocols, on the other hand, invoke a route determination procedure on demand only. Thus, when a route is needed, a global search procedure is employed. The classical flood-search algorithms are typical reactive protocols, such as the Ad Hoc On-Demand Distance Vector Protocol (AODV), which is also known to persons of ordinary skill in the art.
The advantage of proactive protocols is that the route is always pre-calculated, so that there is little delay involved when forwarding data traffic. In reactive protocols, the delay created by the process of determining a route can be quite significant. Furthermore, the global search procedure of reactive protocols requires significant control traffic. An example of how this search procedure is implemented is described in the AODV Protocol. Such route determination delays may also cause data packets to be dropped, unless the device has sufficient capacity to buffer them. Such buffer systems also cause significant implementation complexity. Consequently, pure reactive routing protocols may not be practical for real-time communications in MANETs. However, pure proactive schemes are also not appropriate for MANETs, as they continuously use a large portion of the network's capacity to keep the routing information current, even with the optimization procedure used in OLSR. OLSR uses a procedure called MultiPoint-Relay (MRP) to reduce the flooding control traffic to a certain degree, but it still does not change the fundamental per-node-flooding mechanism.
At the IETF (Internet Engineering Task Force), there is a MANET working group (see http://www.ietf.org/html.charters/manet-charter.html) which is working on a standardizing IP routing protocol functionality suitable for wireless routing applications within both static and dynamic topologies with increased dynamics due to node motion or other factors. The routing protocols that have been standardized by this working group include AODV (RFC 3561), OLSR (RFC 3626), TBRPF (RFC 3684) and DSR (RFC 4728). More detailed information can be found at the website given above.
The IEEE 802.11s working group is proposing two routing approaches: one based on AODV and another one based on an OLSR. These approaches attempt to port the same routing protocol standardized by IETF to a Layer 2 domain. That is, while the basic routing protocol is still the same, the IP addresses have been replaced with Medium Access Control (MAC) addresses, while the IP based routing messages have been replaced with 802.11 Information Elements in 802.11 frames. The AODV approach is used with the hope that it will consume less network resources as long as the topology correctness satisfies the minimum requirement. This approach has the limitation of slow network topology convergence and longer route setup delays, which are very critical to the users of a wireless access network. One of the primary goals when deploying a wireless access network is to support mobility, which means supporting a virtually constantly changing network topology. Slow topology convergence time also indicates a bad network application response time, which is unacceptable for some timing critical applications like Voice Over IP (VOIP). The Ad Hoc On-Demand Distance Vector Routing Protocol, dated July, 2003, and the Optimized Link State Routing Protocol, dated October 2003, are incorporated herein in their entirety by reference.
Some prior art network equipment vendors use an approach called the controller-based Wi-Fi access solution, which depends on a wired architecture to connect all access points back to a central controller. Because of this wired and centralized backhaul network topology, the networking routing challenge disappears, but it does not come for free. The price paid by this sort of network is the limited scalability and system robustness that it provides, which is intrinsic for any centralized approach.
What is needed is a routing protocol that is optimized for static backhaul topologies with mobile stations and based on Layer 2 information similar to the IEEE 802.11s path selection protocol.
What is further needed is a scalable routing method and system that significantly reduces the broadcast control message overhead in a distributed wireless network, while still maintaining fast routing computations that are loop free, to thereby provide a scalable robust wireless access network. After the network route is established, what is also needed is a method and system for eliminating data packet broadcast looping.